Dual-polarized antennas are preferably used in the mobile radio field for 800 MHz to 1000 MHz, and in the band from 1700 MHz to 2200 MHz. The antennas transmit and receive two orthogonal polarizations. In particular, the use of two linear polarizations aligned at +45° and −45° with respect to the vertical or horizontal have been proven in practice. Dual-polarized antennas aligned in this way are also frequently referred to as X-polarized antennas. In order to optimize the illumination of the supply area, without needing to mechanically depress the antenna, the polar diagram is depressed electrically by changing the phase angles of the individual antenna elements of the antenna array. This is done using phase shifters which, owing to the stringent intermodulation requirements and the high transmission power levels, are preferably in the form of mechanically moving structures with variable line lengths. Phase shifters such as these are known, for example, from DE 199 38 862 C1.
Although the possibility of depressing the antenna to different extents by varying the phase angles of the individual antenna elements is intrinsically very highly advantageous for adaptation of the illumination in situ, it has been found to be disadvantageous in the case of antennas having a polarization of +/−45°. However, varying the depression of the vertical polar diagram, that is to say varying the phase angles of the individual antenna elements, shifts the horizontal polar diagrams for the respective polarization through an angle in azimuth.
In this case, it has been found to be particularly disadvantageous that, when the vertical polar diagram depression is changed, the horizontal polar diagrams for the respective polarization are not only shifted but that, particularly when the vertical polar diagram is depressed, the horizontal polar diagrams for the +45° polarization and for the −45° polarization are shifted through an azimuth angle in the opposite directions to one another. This drifting apart from one another in opposite directions for the +45° polarization to the −45° polarization can be explained, inter alia, by the fact that the radiation characteristic of the individual antenna elements is not rotationally symmetrical with respect to the main lobe direction. In other words, the polar diagram of the individual antenna elements in most cases is no longer exactly symmetrical with respect to the vertical axis due to the specific configuration of the polarization of +45° on the one hand and −45° on the other hand. If any axis of symmetry were to be present at all, it would preferably intrinsically run aligned at +/−45° with respect to individual groups of antenna elements. When the main lobe direction of the antenna array is depressed electrically, this now results, however, in the main lobe direction being shifted, which is also referred to as tracking. This thus results in the polar diagram being undesirably dependent on respectively selected depression angles.
The problem which has been explained occurs exclusively in the case of polarizations aligned at oblique angles, that is to say primarily in the case of polarizations which are aligned at +45° and −45° with respect to the horizontal or vertical.
Against the background of this prior art, the technology herein improves a dual-polarized single-band, dual-band and/or multiband antenna array such that, with a depression angle which can be set differently, it is possible to compensate better for, or even to prevent, the polarization-dependent polar diagrams drifting apart from one another.
It is surprising that, according to an exemplary illustrative non-limiting implementation, this makes it possible not only to set the depression angle of a dual-polarized antenna array differently but to reduce, or even completely to avoid, the individual radiation characteristics for the +45° polarization and for the −45° polarization drifting apart from one another as a function of the depression angle, which can be preset to be different.
According to a non-limiting implementation, this can be achieved by also providing a compensation device in addition to the individual antenna element arrangements. These individual antenna element arrangements, for example, are arranged one above the other with a vertical offset, and transmit and receive using two polarizations which are orthogonal to one another, for example +45° and −45°. According to an exemplary illustrative non-limiting implementation, this compensation device is constructed such that it comprises additional antenna elements or antenna element arrangements, whose polar diagrams do not overall drift apart from one another in the azimuth direction when the vertical polar diagram of the antenna array is depressed but, conversely, are shifted in the opposite sense relative to this. This therefore results in an overall polar diagram in which, despite the down-tilt angle being increasingly depressed, that is despite the increasingly greater depression of the vertical polar diagram, the drifting apart of the horizontal components of the polar diagram in the azimuth angle direction is minimized, or even prevented. If required, it would even be possible to provide overcompensation, in which case it would be feasible to provide even a slight angle change in the opposite sense for the horizontal polar diagrams for the +45° to the −45° polarization.
One preferred exemplary non-limiting implementation provides for the compensation device for the relevant polarization to in each case comprise at least one pair of dipole antenna elements or at least one pair of feed points for at least one patch antenna element, which are arranged at least horizontally offset with respect to one another (and possibly also vertically in addition), and which are in this case fed with a phase difference which is dependent on the depression angle of the antenna array. This can preferably be produced by means of a phase shifter assembly located in the antenna.
It may be regarded as being particularly advantageous that it is also possible, in a development of an exemplary illustrative non-limiting implementation, to control the compensation level as well, in order to avoid tracking. The control process may in this case be carried out by splitting the power which is fed to the individual antenna elements.
An exemplary illustrative non-limiting implementation may be implemented using different antenna element types. In this case, furthermore, not only corresponding individual antenna elements but also group antenna elements may be used by an antenna array.
The antenna array may therefore, for example, comprise a number of cruciform dipoles or cruciform-like dipole structures arranged vertically one above the other. The individual antenna element arrangements which are arranged vertically one above the other may likewise all or in some cases comprise dipole squares or dipole structures similar to dipole squares. It is equally possible for an exemplary illustrative non-limiting implementation to be implemented entirely or partially using patch antenna elements which, for example, are provided with a feed structure which comprises two feed points or four feed points, in which case the relevant polarizations can be received or transmitted at angles of +45° and −45°.
Thus, in other words, individual antenna elements which by way of example are located such that they are horizontally offset, or antenna element groups in the antenna array which are located such that they are offset horizontally can be compensated for with respect to one another in order to avoid tracking when their emission angle is depressed, This may be accomplished, for example, by choosing different phase angles for at least two antenna elements, which are located horizontally offset with respect to one another, as a function of the elevation angle or depression angle.
If, for example, square antenna element structures, that is to say in particular square dipole structures in the form of a dipole square, are used, then this antenna element arrangement comprises two individual antenna elements. These two individual antenna element may have a horizontal offset with respect to one another, for each polarization when aligned to receive and to transmit polarizations at angles of +45° and −45°. In this case, the pairs of mutually aligned dipole antenna elements in a dipole square may be driven with a phase difference which is dependent on the depression angle of the antenna array in order to produce the desired compensation effect. This may be done, for example, by the antenna array having only one such dipole square which is used for compensation, or having a number of such dipole squares. This can be implemented in a particularly advantageous manner by an antenna array according to an exemplary illustrative non-limiting implementation comprising, for example, two dipole squares which are arranged vertically one above the other. The respectively parallel adjacent dipoles of the two dipole squares may be arranged vertically one above the other and connected together in phase. That is to say, they may at least being connected together with a fixed phase relationship between them. The respective further dipoles which are parallel to them in the relevant dipole square may be fed with different phase angles as a function of the depression angle.
A solution which is comparable to this extent may also be obtained by using patch antenna elements which, for example, each comprise pairs of interacting feed points for each of the two polarizations.
However, an exemplary illustrative non-limiting implementation may also be used for other antenna structures, for example using cruciform antenna elements (dipole cruciforms or patch antenna elements with cruciform antenna element structures). There, the respectively parallel individual antenna elements may be provided with different components offset only in the vertical direction and possibly not in the horizontal direction. However, in this case, but of course also in the other abovementioned cases, it is at least possible to use additional antenna elements which are arranged with a lateral, horizontal offset. Hence, a further development of an exemplary illustrative non-limiting implementation provides for additional antenna elements to be provided in addition to the other antenna elements which are arranged one above the other, which additional antenna elements are located offset at least horizontally and in this case preferably symmetrically with respect to a vertical axis of symmetry or plane of symmetry, with the relevant antenna elements for each polarization being electrically connected to the associated output of a phase shifter assembly. This also results in a completely novel type of compensation according to the an exemplary illustrative non-limiting implementation which allows the illumination areas to drift apart from one another when the vertical polar diagram is depressed electrically.
The additional antenna elements which are used for the compensation device may thus be produced from dipole structures which are arranged with a horizontal offset. In particular, individual dipoles for example in the form of a cruciform or square dipole structure may be used. Alternatively, a patch antenna element with at least two feed points or two pairs of feed points for each of the two polarizations may be employed. Furthermore, however, it is even possible to use vertically aligned individual antenna elements which are arranged in pairs with a horizontal offset, preferably with respect to a vertical central plane of symmetry. Each pair of vertically aligned individual antenna elements, or a corresponding pair of patch antenna elements, may be provided for each of the polarizations that are to be compensated in a corresponding manner.
In summary, it can thus be stated that the antenna array may comprise widely differing antenna elements and antenna element arrangements whose polar diagrams normally drift apart from one another as the polar diagram is depressed to an increasingly greater extent in the horizontal direction, and hence in the azimuth direction. According to exemplary illustrative non-limiting implementation, compensation devices are provided which are formed from widely differing antenna elements, antenna element arrangements or group antenna elements. Those individual antenna elements or feed points of a patch antenna element can be driven with different phase angles so as to counteract their polar diagrams drifting apart from one another, so as to reduce or even prevent such drifting apart and, if required, even to overcompensate for it. The compensation level can be set or preselected as appropriate by means of the number of antenna elements associated with the compensation device. Power splitting can be carried out in a corresponding manner.